1. Field of the Invention
The present invention relates to a vehicle and a method for operating a battery in a vehicle.
2. Background Art
Batteries, such as traction batteries in hybrid electric vehicles (HEV's), have a finite life. A battery controller can be used to determine when the battery has reached its end of life, and further, to communicate this to the diagnostic system and the driver, and adjust output parameters to the rest of the vehicle control system accordingly. There may be a number of different ways to determine when a battery has reached the end of its life.
One such method for diagnosing the health of a battery is described in U.S. Pat. No. 6,456,043 (Finger). The method described in Finger includes charging a battery that is at least partially depleted, measuring the voltage after the battery has been charged, and comparing the measured voltage to an expected voltage. If the measured voltage falls within some expected voltage range, the battery is determined to be healthy.
One issue that must be addressed in developing a method for determining the end of a battery's life is how to reduce the likelihood of prematurely designating the battery at its end of life. For example, temporary environmental conditions, such as temperature, may have an impact on the output of the battery. Moreover, for a battery that is made up of a plurality of interconnected battery cells, an equalization or “rebalancing” process may need to be periodically performed in order to equalize the state of charge (SOC) across each of the cells. Otherwise, one or two weak cells in the group may provide a false indication that the battery itself is incapable of providing a desired output, and an end of life determination may be prematurely made.
Therefore, it would be desirable to have a method for managing a battery that included a robust end of life determination, such that the end of life determination was not premature, and “false positives” were avoided.